Add note about find_library() not working
- see #796
diff --git a/docs/troubleshooting.rst b/docs/troubleshooting.rst
index bc739cc..1608dec 100644
--- a/docs/troubleshooting.rst
+++ b/docs/troubleshooting.rst
@@ -66,7 +66,9 @@
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
This includes a number of modules that need to start other executables to
function correctly. Examples that have shown this problem include `GitPython`_
-and `plumbum`_.
+and `plumbum`_. Calling ``find_library`` also uses ``subprocess`` and does not work in
+the fake filesystem.
+
The `Pillow`_ Imaging Library
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
